Re: Minimum Depth For Slip?
The printed tables are usually just fine. They're almost all based on the same NOAA predictions and/or algorithms anyway.
My point is that the spring tides vary from month to month. Spring tides occur around the new and full moons, and are the lowest and highest tides during the lunar cycle. They are named because not for the season, but because of the strong resultant currents (the tides seem to "spring" back and forth). The most extreme spring tides tend to be those around the summer and winter solstices. For instance, we're in a spring tide series right now. Near Mission Bay the lowest tide in this particular series will be a -0.65 foot tide Thursday morning. However, the spring tides at the beginning of last month got as low as -1.92 feet. And the tides a week or so before Christmas this year will get down to -1.96 feet. Those extreme spring tides are the ones you need to worry about, rather than the "average" spring tides.
One caveat to keep in mind is that, as an Oceanographer told me many years ago, "Tide predictions are only good to within about a half and hour and a half a foot." In other words, the weather, and simple errors in our models, can influence the actual tide enough to be off by bit. If you surf the NOAA website a bit you should be able to find a trace of the actual tidal level as compared to the prediction for any site with a NOAA "reference station". When the barometric pressure is high, it tends to push the tidal level down a bit. When the pressure is low, it tends to pull the tide up a bit. Winds also have a bit of an effect, particularly in embayments.
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Last edited by SlowButSteady; 07-18-2012 at 03:13 AM.